Field of the Invention
The subject of the present invention is a sealing ring for a hydraulic pump distributor.
Description of the Related Art
Rotary cylinder axial-piston or radial-piston hydraulic pumps, particularly those of variable cylinder capacity, are usually made up of a rotor in which hydraulic cylinders are formed. Within each of the said cylinders, a hydraulic piston performs reciprocating movements.
The said rotor ordinarily comprises a feed face kept in the most sealed possible contact with a distribution face—also sometimes known as a distribution plate—formed at the surface of a stator, it being possible for the latter to form part of a pump body.
The feed face generally comprises orifices each connected to one of the hydraulic cylinders, whereas the distribution face comprises at least one inlet port via which the hydraulic pistons can draw in a hydraulic fluid and at least one delivery port via which the said pistons can deliver the said fluid, the said orifices and the said ports constituting a hydraulic distributor.
Thus, as the rotor turns, the said orifices are alternately brought into communication with an inlet duct by the inlet port then with a delivery duct via the delivery port. The result of this is that a flow of hydraulic fluid may become established between the said ducts as a result of the reciprocating movements that the hydraulic pistons perform, each one in its own hydraulic cylinder.
It will be noted that leaks of hydraulic fluid unavoidably occur between the feed face and the distribution face. As a result, some of the hydraulic fluid passes directly from the delivery duct to the inlet duct or vice versa, on the one hand, while some of the said fluid passes directly from the said ducts to an internal housing that the said hydraulic pumps generally comprise, on the other hand. These leaks reduce the volumetric and energy efficiency of the said pumps.
In the case of hydraulic pumps of the type having axial pistons, in order to be as sealed as possible with respect to one another, the feed face and the distribution face are subjected to a load which tends to keep them in contact with one another. This load is notably the result of the reaction force generated by a thrust plate in response to the thrust of the hydraulic pistons, it being possible for example for the said plate to be a swashplate or a yoke.
Combined with the relative movement of the said faces, the said reaction force results in friction losses which reduce the energy efficiency of the pumps designed in this way. It must be pointed out that, in the particular case of axial-piston hydraulic pumps, the feed face and the distribution face are each positioned on a planar circular surface.
In the case of rotary cylinder radial-piston hydraulic pumps, the distributor is usually made up of a distribution face positioned on the external surface of a first cylinder secured to the stator, whereas the feed face is positioned on the internal surface of a second cylinder which fits over the first cylinder and is secured to the rotor. With this particular configuration, sealing between the said faces is preferably obtained by a small clearance left between the first and second cylinders, extreme precision being required in the machining of these cylinders during manufacture.
Obtaining sealing using this strategy leads to significant leaks that occur at this latter type of distributor, even though the friction losses generated by the said distributor are potentially lower. Furthermore, unless the radial-piston hydraulic pump is radially balanced with at least two inlet ports and two delivery ports which are diametrically opposed, the pressure exerted by the hydraulic fluid on the cross section of the port subjected to the higher pressure may subject the said distributor to what can be a potentially high radial load that may cause not-insignificant additional friction losses.
This disadvantage can be lessened if not practically eliminated if radial-load equalizing grooves are provided to counterbalance the radial load of the inlet or delivery port that is subjected to the higher pressure. Such an arrangement is, for example, set out in the patent application relating to a pump motor U.S. Pat. No. 1,354,562 dated May 22, 2013, in the name of the applicant.
Bearing in mind the foregoing, in the current state of the art, a distributor with a high level of sealing tends to generate high friction losses whereas, conversely, a distributor with low friction losses is rather inclined to exhibit significant leaks of hydraulic fluid.
It may be noted that the relative drop in energy efficiency caused by the hydraulic leaks and by the friction losses occurring between the feed face and the distribution face of rotary cylinder radial-piston or axial-piston hydraulic pumps, notably those of variable cylinder capacity, is higher if the pressure at which the said pumps operate is higher, on the one hand, and if the said pumps are used at partial cylinder capacity, on the other hand.
It is therefore particularly important to reduce the said leaks and the said losses as far as possible while at the same time recovering the highest possible fraction of the energy released by the hydraulic fluid as it decompresses.